Slow-Cooked Marmalade

• 3–4 lb / 1.35–1.80 kg citrus fruits, including at least a couple of Seville oranges and 1–2 lemons<

Put the whole fruit in a large, heavy pan, cover with water, bring to simmering point, cover and cook on the lowest possible heat for 6–8 hours. Remove from the heat, keep covered, and leave overnight. Next day, measure out 1½ pt / 850